1. Field of the Invention
This invention pertains in general to the detection of cancer in various types of human tissue and, more particularly, to a novel procedure and instrumentation for in-vivo detection of cancerous cells using fluorescence excitation in tissue that is optically accessible for examination.
2. Description of the Related Art
Several techniques and instruments have been described by investigators for the purpose of detecting cancerous cells. For example, U.S. Pat. No. 5,062,431 to Potter (1991) utilizes in-vivo fluorescence detection of abnormal tissue by irradiating a photosensitized diagnostic region simultaneously with at least two excitation wavelengths. Fluorescent light emitted from the diagnostic region is detected and a signal is generated relating to the intensity of the fluorescence. A difference signal between the two wavelengths is used to distinguish the fluorescence of normal tissue from that of diseased cells.
In U.S. Pat. No. 5,106,387 (1992), Kittrell et al. disclose a method for identifying atheromaterial in a vascular lumen for diagnosis of arterial or vascular obstructions. Diagnosis is accomplished by spectrally analyzing the return radiation with or without a reference spectrum. U.S. Pat. No. 5,115,137 to Andersson-Engels et al. (1992) describes a method for detecting atherosclerosis and blood disorders by utilizing fluorescence excitation at wavelengths less than 500 nm. The intensity of a plurality of wavelengths, at least two of which have substantially equal absorption by blood, is used to evaluate the character of the tissue being tested.
U.S. Pat. No. 5,131,398 to Alfano et al. (1992) describes diagnosis of cancerous cells by using a substantially monochromatic excitation light and two detection bands at about 340 and 440 nm of the fluorescent emissions. The ratio of the fluorescent intensities at the two wavelengths for normal tissue is then calculated and used as a reference for comparison for identifying cancerous tissue. The invention is based on the discovery that when tissue is excited with monochromatic light at wavelength of about 300 nm, the resulting native fluorescence spectrum over the region from about 320 nm to 600 nm in cancerous tissue is substantially different from that of either benign or healthy tissue. The patent further teaches that avoiding the use of fluorescent emissions between about 380 nm and 430 nm, one can ignore the effect on the fluorescence intensity resulting from blood absorption. In addition, the patent teaches that at excitation wavelengths above 315 nm the ratios of fluorescent-emission intensities are indistinguishable between cancerous and benign cells.
In spite of the progress illustrated by the prior art, it still remains difficult to identify cancerous tissue by direct in-vivo examination. The use of monochromatic or narrow bandwidth for excitation and emission light (such as the 20 nm bandwidth taught by Alfano et al.) requires sophisticated and expensive instrumentation capable of detecting very low light intensities and of functioning with low signal-to-noise ratios. Therefore, it would be very useful to devise a technique that allows the use of wideband radiation and reception and that produces visible light signals for manual operation of the detection instrument. The present invention is directed at providing such improvements to prior-art devices and procedures.